Electronic switching of ignitron tubes for heavy loads



Juhe 15, 1954 S. C. ROCKAFELLOW ELECTRONIC SWITCHING OF IGNITRON TUBES FOR HEAVY LOADS 2 Sheets-Sheet l Fild April 16, 1953 INVENTOR.

Swan?- 6. Rama/21w June 15, 1954 s. c. ROCKAFELLOW ELECTRONIC SWITCHING OF IGNITRON TUBES FOR HEAVY LOADS 2 SheetS-Sheet 2 Filed April 16. 1953 INVENTOR. 571/527" 6. Roc/mraww HTTORNEY of alternately energized ignitrons.

Patented June 15, 1954 ELECTRONIC SWITCHING OF IGNITRON' TUBES FOR HEAVY LOADS Stuart 0. Rockafellow, Farmington, Mich.,- assignor to'Robotron Corporation Application April 16, 1953, Serial N02 349,136-

10 Claims. 1

This invention relates to an ignition system for ignitron tubes as used in resistance welding service and it'more particularly'relates to an electronic switching system for igniting alternate pairs of ignitron'tubes, such alternate pairs being used to decrease the average load-carried by each'of said 'pairs.

In the designing'of electric welding circuits utilizing ignitron tubes,'it is'well recognized that the current carrying capacity of such tubes is governed by what is termed a duty cycle. For example, if a set of'ignitrons carries 1000 amperes of current for 0.2 second in a-2 seconds on-off cycle, this would bereferred to as a 10% duty cycle. If the'same tubes'were'then caused to carry current for 0.4. second in a 2 seconds on-off cycle, this would constitute a '20 duty. cycle and the safe tube rating. as established by the manufacturer would be materially less; as about-500 ampere's of current.

On large loads, even'the largest'size of ignitrons commercially available are too small to carry the required loads at the cycles required and the amount of time that each 'set' of ignitrons is conductive is reduced by using two sets In this manner, it becomes possible to handle "substantially double the amperages which would otherwise be passed through a single set.

In previous attempts to utilize this pattern-for connecting ignit'rons in a Welding circuit,'reliance has been pl'acedon mechanical relays to change the firing from one set of ignitrons to the other. However, the mechanical difficulties,- particularly including the'relatively short life, of such relays have seriously limitedthe usefulness of 'thistype of circuit.

Accordingly, a -major object ofthe invention is to provide a circuit for alternatelyfiring two parallel connected sets of ignitrons without the necessity of using any mechanically moving parts.

A further object of the invention is to provide a circuit, as aforesaid, without theneed' for' using relays.

A further object of the invention is to provide a circuit, as aforesaid, which is adaptable for use with phase shift control.

A further object of the invention is to provide a circuit, as aforesaid, in which a. large number of different types of circuits maybe used. as the timing and controlling medium.

A further object 'of the inventionis to provide a' circuit, as aforesaid, in which the timing and controlling medium employs a conventional flip- A further object of the invention isto provide "a circuit, asaforesaid', which will be subject to close adjustment and'which, when'adjusted, will not readily get outof adjustment.

A further object of the invention is to provide a circuit, as aforesaid, which is capable of being built with sturdy apparatus and hence will have lowmaintenance requirements.

Other objects and purposes of the invention will be apparent to persons acquainted with circuits of thisgeneral type upon a reading of the following description and an inspection of the accompanying drawings.

In the drawings:

Figure l constitutes a circuit diagram of'apparatu'sembodying the invention.

Figure 2 constitutes a fragmentary circuit diagram of a modification.

In general, a thyratron firing circuit is provided for each of the ignitrons. The conductivity of the firing thyratrons associated with one pair of ignitrons is'controlled by a phase shift circuit including two switching thyratron's' as resistance elements therein. The conductivity of the firing thyratrons controlling the other pair of 'ig'nitrons is controlled by a second phase shift circuit similarly including two further switching thyratrons as resistance elements therein. An electronic circuit, as a flip-flop circuit, provides a potential alternating between the grids of the switching thyratrons with respect to their respective cathodes; and thereby renders conductive alternate pairs of firing thyratrons and'of their associated sets of ignitrons.

Referring now to Figure 1 in detail, the source conductors land"? are connected to opposite terminals of any convenient source of alternatingipotential, as ll0'volt, 6U cycle. The conductor 2 is connected through the primary winding 3 of the welding transformer 4 and thence through the parallel connected sets 6 and 1 of back-to-back connected ignitron'sto the conductor i. Eachof said ignitro'ns 8, 9, and. I2 'is provided with any con venient type of transformer nous are made With respect 'tothe firing thymtrons I8, I9 and 2I and the respectively connected secondary windings 22, 23 and 24 of the transformers IB and 26.

All of the foregoing circuitry is conventional and will be so recognized by those skilled in the art.

Turning now to the control circuitry which is the particular subject matter of the present invention, the transformers 2'! and 28 are connected by their primary windings 29 and 3I respectively in parallel with each other and between the source conductors I and 2. An initiating switch 32, which may be another electronic circuit, will normally be provided to initiate operation of the control circuit and thereby initiate conduction of the ignitrons.

Connected to the secondary winding 33 of the transformer 21 is a phase shift circuit 30 of any convenient type utilizing electric discharge devices as resistance elements thereof. In the cir cuit here shown, there is a capacitor 34 and a resistance circuit 36 connected in series with each other and with said secondary winding 33. The resistance circuit 36 includes the rectifiers 31 and 38 connected in opposite polarity with respect to each other and in series with each other and with the terminals 39 and II of said resistance circuit. A pair of switching thyratrons 42 and 43 are each connected by their anodes respectively to the terminals 39 and M and the cathodes of said switching thyratrons 42 and 43 are connected each to the conductor 44. A conductor 46 including a variable resistor 45 connects a point intermediate said two rectifiers with a point intermediate the cathodes of said two thyratrons 42 and 43. The output terminals I3 and I4 are connected to the primary winding I8 of the transformer 26.

The secondary winding 29 of the transformer 28 is connected to a similar phase shift circuit 35 including the capacitor 41 and the resistance circuit 48. Said resistance circuit 48 includes the switching thyratrons 49 and which are connected into the phase shift circuit 35 and to the conductor 44 in the same manner as the switching thyratrons 42 and 43 are associated with the resistance circuit 36 and hence need no further detailing. The grids of the thyratrons 42 and 43 are connected together and connected to a com ductor 52 and the grids of the thyratrons 49 and I 5I are connected together and to the conductor 53. The output terminals 16 and I1 are connected to the primary winding I9 of the transformer I6.

.Any convenient circuit 54 is provided for supplying a constant positive potential to the conductor 44 and a potential, which is negative with respect to the potential supplied to conductor 44, alternating between the conductor 52 and the conductor 53. In the particular embodiment here utilized to illustrate the invention, the circuit 54 comprises a conventional flip-flop circuit. The conductor 44 is connected to the positive side of a source 56 of constant potential, as a battery,

and the negative side of said source is connected to the cathodes of a pair of thyratrons 51 and 58. The anodes of said last-named thyratrons are connected to the conductors 53 and 52. A capacitor 59 is connected between the anodes of said thyratrons 51 and 58. The conductor 44 is connected through a resistance 5| to the anode of the thyratron 51 and also by the conductor 62 through a variable resistance 63 and a capacitor 64 to the grid of the thyratron 58. Said lastnamed grid is also connected through a resistance 66 to the cathode of said thyratron 58. The conductor 44 is also connected through the resistance 61 to the anode of the thyratron 58 and is also connected by the conductor 68 through the variable resistor 39 and the capacitor II to the grid of the thyratron 5'I. Said last-named grid is also connected through a resistor I2 to the cathode of the thyratron 51.

The modification shown in Figure 2 illustrates a different type of circuit for resistance circuits 36 and 48. All of the parts of the circuit of Figure 2 which are identical with the parts of Figure l are designated by like numerals and need no further description. Further, said circuit connects to an ignitron circuit of the same nature as shown in Figure 1 and hence needs no further detailing. The resistance circuits utilized in this circuit are indicated at 36a and 48a and function with respect to the rest of the apparatus in the same manner as the circuits 36 and 48 of the circuit of Figure l. The resistance circuits 38a and 480; themselves, however, are here shown as saturable reactors 83 and 84 having D. C. windings 35 and 85, respectively. With the D. C. windings deenergized, the resistance of the resistance circuits is high and a substantial phase shift is effected. With the D. C. windings energized, the resistance becomes negligible and the phase shift is at a minimum.

Operation Considering first the at rest condition of the apparatus shown in Figure 1, namely, with the switch 32 open, the phase shift circuits will be deenergized and the constant bias in each of the grid circuits of the ignitron firing thyratrons I3, I8, 59 and 24 will hold said thyratrons non-conductive. Thus, the respectively connected ignitrons will be non-conductive.

With the closing of the switch 32, the transformers 21 and 28 will become energized and will place alternating potentials on the output terminals I3, I4, I6 and 11 of the phase shift circuits. Assuming now that there is no phase shift efiected in the phase shift circuit 30, the primary winding I8 of the transformer 26 will be energized substantially in phase with the energization of the source conductors I and 2, thereby energizing the secondary windings 23 and 24 of said transformer. This will overcome the constant bias in the grid circuits of the thyratrons I9 and EI and thereby cause same to become conductive which in turn will fire the ignitrons II and I2 substantially in phase with the potentials placed on their principal electrodes and they will conduct. Similarly, energizing of the phase shift circuit 35 will energize the primary winding I9 of the transformer I6 substantially in phase with the source conductors I and 2 and this in turn will overcome the constant bias in the grid circuits of the thyratrons I3 and I8. This will render said thyratrons conductive and fire the respectively connected ignitrons 8 and 9 substantially in phase with the potentials placed on their principal electrodes and they will conduct. Since the tubes 42, 43, 49 and 5! are of gas-filled type, there will be no gradual shift in phase output of the phase shift circuits but rather the phase shift circuits will produce output potentials of either fully phase shifted characteristics or substantially non-shifted characteristics insofar as the tubes 42 and 43 are concerned. However, if desired, the variable resistance 45, here shown as a single element but which may also be another electronic circuit, may be utilized to control the minimum resistance in said resistance circuit -36 when said switching thyratrons are' conductive and-thus-control the maximum heat produced at the-welding electrodes;

The fiip-flop-circuit tsi will act in response to the negative potential applied by the battery 56 toproduce alternate negative potentials on the conductors 52 and53. Thus; theswitching thyratrons' 42 and 3 will be blocked'at' one given instant-and the tubes 49' and iii will be conductive. In this condition the'phase shift circuit 3U--will effect amaximum' phase shift of the output of the transformer 2'6with respect to the input thereof and this-will fail to overcome the blocking'potentialapplied to the firing thyratrons i-aand'zl. Thus; the pair 1 of ignitrons will be non-conductive. Atthe same moment; withthe switching thyratrons 49 and 5i conductive, the output ofthe-pha-seshift circuit 35 will be substantially in phase with the input thereof and hence-the secondary windings It and 22 will overcome the blocking bias otherwise applied to the'thyratrons i3 and 48; said thyratrons will 'be conductive and the pair s of ignitrons-will also be conductive.

As soon as the potential on the conductors 52 and 53 reverses with respect to the potential on the'conductor i i, then the phase shift will appear in-the phase -shift circuit 35 and the pair 6 of ignitrons will be non-conductive. At the same time a minimum phase shift will appear in the phaseshift circuit-Wand the pair i of ignitrons will be conductive.

The conduction of either pair of ignitrons will so diminish the potential between the junction points- 8-l and 82 as to preclude conduction by the other pair of ignitrons. Thus, after one phase shift circuit has fired one pair of ignitrons, a'subsequent firing potential appearing from the other phase *shift'circuit on the other pairof ignitronswill have no effect. Accordingly, there isno possibility of overlapping of firing bythe respective pairs of 'ignitrons. Further, each pair of ignitrons, when once started, will continue conducting untilthe anode potential falls below a minimumlevel.

Thus, if the output of the flip-flop circuit 54 changes the potential appiied to the phase shift circuits at a-point-of time intermediate the zero points of a given waveform applied to the conductors l and 2; conduction will continue in the-pair of ignitrons then conducting until the potentialbetween the conductors l and 2 returns substantially to Zero and conduction will commence in the other pair promptly upon the reverse potential appearing betweensaidconductors l and 2. Hence, there can be no overlapping of firing of respective pairs 'of ignitrons, nor can therebe appreciable gaps between the firing of such respective pairs and the supply of welding current passed by said justable. by adjustment of the variable resistors -65Jand'69 whichxfor uniformity'may, if'-desired,., r

be connected for simultaneous adjustment by a single control.

Thus, a circuit has been provided by which an entirelyelectronic means-will ren'der thepaii' 6 and the pair I of ignitrons alternately conduc tive and that the respective periods of conduce tion andnon-conduction of-each is :readily'zcon trollable.

In the form of the inventionshown'in Eigure 2, the'saturable reactors=83 and 8'4 perform:the switching functions of the switching-'thyratrons, 42, 43, Hand 5+ in response to thesoutputliof the circuit 5c in the manner'above: described. The'remainder of the circuitfunctions inithe same manner as above described in connection with the circuit of Figure 1.

While I have employed a specific embodiment for illustrating the invention, it will berecognized that many variations may be made-from the specific circuit here shown, as will'be' recoge nized by those acquainted with the art, and th'at such variations will be included withinthe'sc'ope of the hereinafterappended claims, excepting as said claim may by their own terms expressly require otherwise.

I claim:

1. A circuit forfiring two parallel connected pairsof back-to-back connected ignitrons in-a load circuit, the combination comprisingnfirst and second transformers each having twotisecondary windings; four circuits eachincluding a firing thyratron connected one with eachig nitron for firing same and each includingone of said secondary windingstherein so connected that energization of said secondaryuwindings will render conductive the firingthyratronsxrespectively connected thereto and thereby fire the ignitron associated therewith; the twoisecondary windings so associated with one pai-rrof ignitrons being of. said first transformer and the two secondary windings so' associated with the other pairofignitrons being" of the?'0the1' transformer; first andsecond phaseshiftcircuits, each including a resistance elementtherein, said resistance elements each =includingiswitchingrmeans becoming conductive or non-conductive in'response to ail-independentpotential'applied thereto; conductors connecting theprimary winding of each of said transformers with the pairs of back-to-back connectedignitrons'in .a

load circuit, the. combination comprising: first and second transformers each having two .sec-

. ondaryswindings; four circuits eachincludinga firing thyratron connected one with each'ignitron for firing same and each including. oneofsaid secondary windings therein so connected that energization of. said secondary windings; will render conductive the firing thyratrons respectively connected thereto and thereby fire the.-ig nitrons. associated therewith, and: the two secondary windings so associatedwith onepairof ignitrons being. of said first transformer. and the two. secondary windings sov associatedwith; the other pair: of ignitrons. being of: the other :transformer; first. and. second: phase; shift circuits,

each having a resistance component therein, said phase shift circuits each including a pair of switching thyratrons as said resistance component; a control conductor connecting the cathodes of said switching thyratrons; conductors connecting the primary winding of each of said transformers with the output terminals of each respective phase shift circuit; a source of constant voltage, the positive side thereof being connected to said control conductor and Wholly electrical ,gization of said secondary windings will render conductive the thyratrons respectively connected thereto and thereby fire the ignitron associated therewith, the two secondary windings so associated with one pair of ignitrons being of said first transformer and the two secondary windings so associated with the other pair of ignitrons being of the other transformer; first and second phase shift circuits, each having a resistance element therein and each of said phase shift circuits each including a pair of gas-filled electric discharge devices as said resistance element; a control conductor connecting the cathodes of said electric discharge devices; conductors connecting the primary winding of each of said transformers with the output terminals of each respective phase shift circuit; a source of corn stant voltage, the positive side thereof being connected to said control conductor and means in cluding a flip-flop circuit connecting the negative side of said source alternately first to the grids of one pair of electric discharge devices and then to the grids of the other pair of electric discharge devices.

4. A circuit for firing two parallel connected pairs of back-to-back connected ignitrons in a load circuit, the combination comprising: first and second transformers each having two secondary windings; two circuits each respectively including a firing thyratron having its principal electrodes connected to the anode and starting electrode of each ignitron and eachfiring thyra tron having a secondary winding of one of said transformers and a source of constant bias potential in the grid-to-cathode circuit thereof; two further circuits each including a firing thyratron having its principal electrodes connected to the anode and starting electrode of the other ignitron and each thyratron having a secondary winding of the other of said transformers and a source of constant bias potential in the grid-tocathode circuit thereof; first and second phase shift circuits, each having a resistance component therein and each of said phase shift circuits each including at least one switching thyratron as said resistance component; a control conductor connecting the cathodes of said switching thyratrons; conductors connecting the primary winding of each of said transformers with the output terminals of each respective phase shift circuit; a source of constant voltage, the positive side thereof being connected to said control conductor and wholly electrical means connecting the negative side of said source alternately to one and the other of the grids of said switching thyratrons.

5. A circuit for firing two parallel connected pairs of back-to-back connected ignitrons in a load circuit, the combination comprising: first and second transformers each having two secondary windings; two circuits each respectively including a firing thyratron having its principal electrodes connected to the anode and starting electrode of each ignitron and each firing thyratron having a secondary winding of one of said transformers and a source of constant bias potential in the grid-to-cathode circuit thereof; two further circuits each including a firing thyratron having its principal electrodes connected to the anode and starting electrode of the other ignitron and each thyratron having a secondary winding of the other of said transformers and a source of constant bias potential in the grid-tocathode circuit thereof; first and second phase shift circuits, each including a resistance element therein, said resistance elements each including switching means becoming conductive or non-conductive in response to an independent potential applied thereof; conductors connecting the primary winding of each of said transformers with the output terminals of each respective phase shift circuit; a source of constant voltage, the positive side thereof supplying one side of said independent potential for each of said switching means and wholly electrical means connected to the negative side of said source and supplying the other side of said independent potential for alternately one and the other of each of said switching means.

6. A circuit for firing two parallel connected pairs of back-to-back connected ignitrons in a load circuit, the combination comprising: first and second transformers each having two secondary windings; two circuits each respectively including a firing thyratron having its principal electrodes connected to the anode and starting electrode of each ignitron and each firing thyratron having a secondary winding of one of said transformers and a source of constant bias potential in the grid-to-cathode circuit thereof; two further circuits each including a firing thyratron having its principal electrodes connected to the anode and starting electrode of the other ignitron and each thyratron having a secondary winding of the other of said transformers and a source of constant bias potential in the grid-to-cathode circuit thereof; first and second phase shift circuits each having a re sistance component therein, said phase shift circuits each including a pair of switching thyratrons as said resistance component; a control conductor connecting the cathodes of said switching thyratrons; conductors connecting the primary winding of each of said transformers with the output terminals of each respective phase shift circuit; a source of constant voltage, the positive side thereof being connected to said control conductor and wholly electrical means connecting the negative side of said source alternately to one and the other of the grids of said switching thyratrons.

7. A circuit for firing two parallel connected pairs of back-to-back connected ignitrons in a load circuit, the combination comprising: first and second transformers each having two secondary windings; two circuits each respectively including a firing thyratron having its principal electrodes connected to the anode and starting electrode of each ignitron and each firing thyratron having a secondary winding of one of said transformers and a source of constant bias potential in the grid-to-cathode circuit thereof; two further circuits each including a firing thyratron having its principal electrodes connected to the anode and starting electrode of the other ignitron and each thyratron having a secondary winding of the other of said transformers and a source of constant bias potential in the grid to-cathode circuit thereof; first and second phase shift circuits each having a resistance element therein and each of said phase shift circuits each including a pair of gas-filled electric discharge devices as said resistance element; a control conductor connecting the cathodes of said electric discharge devices; conductors connecting the primary winding of each of said transformers with the output terminals of each respective phase shift circuit; a source of constant voltage, the positive side thereof being connected to said control conductor and means including a fiip-flop circuit connecting the negative side of said source alternately first to the grids of one pair of electric discharge devices and then to the grids of the other pair of electric discharge devices.

8. A circuit for firing two parallel connected pairs of back-to-back connected ignitrons in a load circuit, the combination comprising: first and second transformers each having two secondary windings; four circuits each including a firing thyratron connected one with each ignitron for firing same and each including one of said secondary windings therein so connected that energization of said secondary windings will render conductive the firing thyratrons respectively connected thereto and thereby fire the ignitron associated therewith, the two secondary windings so associated with one pair of ignitrons being of said first transformer and the two secondary windings so associated with the other pair of ignitrons being of the other transformer; first and second phase shift circuits each having a resistance component therein and said phase shift circuits each including a pair of saturable reactors as said resistance components; a control conductor connecting one side of one of said saturable reactors to one side of the other of said saturable reactors; conductors connecting the primary winding of each of said transformers to the output terminals of each respective phase shift circuit; a source of constant voltage, one side thereof being connected to said control conductor and wholly electrical means connecting the other side of said source alternately to the other respective sides of one and the other of said saturable reactors.

9. A circuit for firing two parallel connected pairs of back-to-back connected ignitrons in a load circuit, the combination comprising: first and second transformers each having two secondary windings; two circuits each respectively including a firing thyratron having its principal electrodes connected to the anode and starting electrode of each ignitron and each firing thyratron having a secondary winding of one of said transformers and a source of constant bias potential in the grid-to-cathode circuit thereof; two further circuits each including a firing thyratron having its principal electrodes connected to the anode and starting electrode of the other ignitron and each thyratron having a secondary Winding of the other of said transformers and a source of constant bias potential in the grid-tocathode circuit thereof; first and second phase shift circuits each having a resistance component therein and said phase shift circuits each including a pair of saturable reactors as said resistance components; a control conductor connecting one side of one of said saturable reactors to one side of the other of said saturable reactors; conductors connecting the primary winding of each of said transformers to the output terminals of each respective phase shift circuit; a source of constant voltage, one side thereof being connected to said control conductor and wholly electrical means connecting the other side of said source alternately to the other respective sides of one and the other of said saturable reactors.

10. A circuit for rendering conductive two parallel connected pairs of back-to-back connected ignitrons in a load circuit, the combination comprising: first and second transformers each having two secondary windings; four circuits each including a firing electric discharge device connected one with each ignitron for firing same and each including one of said secondary windings therein so connected that energization of said secondary windings will alter the conductivity of the firing thyratrons in such a manner as to efiect firing of the ignitron associated therewith, the two secondary windings so associated with one pair of ignitrons being of said first transformer and the two secondary windings so associated with the other pair of ignitrons being of the other transformer; first and second phase shift circuits each including a resistance element therein, said resistance elements each including switching means becoming conductive or non-conductive in response to an independent potential applied thereto; conductors connecting the primary winding of each of said transformers with the output terminals of each respective phase shift circuit; a source of constant voltage, one side thereof supplying one side of said independent potential for each of said switching means and wholly electrical means connected to the other side of said source and supplying the other side of said independent potential alternately to one and the other of each of said switching means.

No references cited. 

